The present invention concerns a method of visualization of a part of a three-dimensional image.
In the medical field, for example, three-dimensional images are frequently used to make diagnoses. In the field of radiology, notably a three-dimensional image can embrace a multitude of interlaced blood vessels. During an examination, a radiologist may want to isolate a part of the image which seems of interest in order to visualize it in detail and establish a diagnosis. A side pocket formed by dilation of an arterial wall, an aneurysm in other words, may be hard to visualize in a three-dimensional image, especially when that pocket is hidden by a multitude of blood vessels. Even several rotations of the three-dimensional image in space do not always make it possible to visualize the aneurysm at a favorable angel. The same is true for the visualization of other pathologies such as stenosis.
There are known methods, described below, making it possible to isolate a part of a three-dimensional image.
It is known how to create zoom effects on an element of interest contained in a three-dimensional image, but the image thus obtained after zooming is not always of very good quality, owing to the fact that for small elements of interest it is necessary to make several enlargements (zoom).
Methods are also known for isolating a part of a three-dimensional image by cut planes. For this purpose, from a given three-dimensional image a cut plane is chosen by tracing a straight line on the three-dimensional image display window by means of a cursor. Thus, the part of the image present, for example, below the line traced is removed from the image. A new three-dimensional image is obtained which is identical to an upper part of the original three-dimensional image.
Finally, the virtual scalpel method is known, making it possible to isolate a part of the three-dimensional image. The isolated part is determined with a free form. The radiologist determines any form by tracing a polygon on the three-dimensional image. The volume taken into account is a cylinder of section identical to the polygon and of infinite length in the direction perpendicular to the display window. A three-dimensional image is then obtained in which only the parts contained in the volume defined by the cylinder are visualized. However, this method has numerous disadvantages, namely:
a lack of interactivity owing to the fact that the parts not visible are no longer accessible, the form obtained cannot be modified and another view necessitates tracing the polygon once again;
failure to control the final volume, since the tracing is done is two dimensions and the lines of the tracing are interpreted in three dimensions according to particular rules;
slowness due to “manual” tracing of the polygon.